It's a topic so divisive that it has been known to be a significant factor in choosing a spouse: Do you let your pet sleep in your bed with you? In some households, it's the norm. All pets are allowed everywhere, all the time. In others, it's no pets on any furniture, ever. But in many, the answer lies somewhere in between: Perhaps the cat or small dog is given a spot to snuggle, but the Great Dane has to remain on the floor. Many factors come into play, of course. Some pet owners suffer from allergies and sleeping with...